Once I start a TV show, if I menu out of it to anywhere else in the application before finishing watching it, when I come back, the episode is no longer showing on the list. I have to change from Sort Method List:Unwatched to List: All Videos to see the episode (which is correctly shown as partially watched). The unwatched counter in each level (show/season) does correctly show the episode as not yet completed.

I am pretty sure that this an issue with how Plex is supported, as it doesn't happen with the native library. Is there a way to fix this?

this is Plex database, I see partially unwatched items... I am misunderstanding what the issue is?

if unwatched only is selected then partially watched shows don't appear. people want partially watched shows to appear in the unwatched list (with triangle signifying partially watched) until they are fully watched.